Channel Mobility in GaN Hybrid MOS-HEMT Using SiO2as Gate Insulator

Abstract

The channel mobility in SiO2/GaN hybrid metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs) has been studied. The formalism used for the inversion mobility in MOSFETs has been adapted to the case of GaN MOS-HEMTs, which operate in accumulation condition. Using the values of interface trapped charges ( ${Q}_{{ {\,trap}}} = {1.35} \times {10}^{12}$ cm $^{{ {-2}}}$ ) and surface roughness (RMS = 0.15 nm) determined by capacitance-voltage measurements and nanoscale morphological analyses allowed to derive meaningful physical parameters for the mobility model. The temperature dependence of the peak mobility—that decreases from 110 cm $^{{ {2}}}\text{V}^{ {-1}}\text{s}^{{ {-1}}}$ at room temperature down to 91 cm $^{{ {2}}}\text{V}^{{ {-1}}}\text{s}^{{ {-1}}}$ at 423 K—is mainly ruled by phonon and Coulomb scattering effects. The implications in practical devices were discussed, considering the possible improvement of the device on-resistance that can be obtained by reducing the interfaces state density at the SiO2/GaN interface.